Wet processing of coffee
To be viable in Australia, mechanised production systems must produce high quality coffee through wet-processing. Previously this has been very difficult to achieve. Machine-harvesting in Australia may require up to three harvester passes, producing a mixture of immature, prime and overmature cherry. While the proportion of prime cherry harvested will increase as harvester technology, harvest management and flowering synchronisation improve, it is unlikely that prime cherry will ever consistently comprise more than 70% to 85% of machine-harvested cherry This means that wetprocessing systems must be able to remove immature and overmature cherry to maintain quality.
Removal of immature cherry is the key issue in processing machine harvested coffee. Overmature cherry can be separated by flotation, but it is difficult to physically separate immature cherry. Experience during trials has shown that conventional equipment cannot accommodate the levels of immature cherry typical of machine-harvesting. Electronic colour sorting of cherry has been investigated but is very expensive because several units are needed to handle coffee from just one harvester (5,000 kg/h) at expected reject rates of 10% to 20% immature cherry.
Water requirements for wet-processing
The water requirements and the pollution potential of wet-processing are considerations in the design and siting of processing factories. The pilot system at Walkamin Research Station uses about 10,000 L/h ofwater to process machine-harvested cherry at 6,000 kg/h. This does not include fermentation and washing which may require an additional 4,000 to 10,000 litres of water for each tonne of dry green bean, depending on the sophistication of the system used.
The pollution potential of waste water is significant. Treatment includes solids removal, settlement and subsequent pondage, or land-based disposal. The design and management of treatment works requires professional expertise and needs to comply with relevant authority regulations. Pulp, discarded cherry and solids separated from waste water are commonly returned to the plantation by spreading under trees or between rows (mulching).
Processed Australian coffee beans
The Walkamin Processing System
Machine-harvested coffee requires a specialised processing system. Such a system has been developed in Australia and can produce high quality coffee from prime cherry regardless of the levels of immature cherry harvested. Limits to the amount of immature cherry handled by the system will be imposed by the economics of harvesting high levels of immature cherry rather than by performance limitations of the system. In developing a system for the wet-processing of machine harvested coffee, Australian researchers have taken a new approach. The key elements of the Walkamin system are innovative and unconventional for coffee processing. See The Walkamin Processing System article for more information.
Source
Craig Lemin
